Barnacles and fucoids on moderately exposed shores

01-10-2000
Researched byJacqueline Hill Refereed byThis information is not refereed.
EUNIS CodeA1.21 EUNIS NameBarnacles and fucoids on moderately exposed shores

Summary

UK and Ireland classification

EUNIS 2008A1.21Barnacles and fucoids on moderately exposed shores
EUNIS 2006A1.21Barnacles and fucoids on moderately exposed shores
JNCC 2004LR.MLR.BFBarnacles and fucoids on moderately exposed shores
1997 BiotopeLR.MLR.BFBarnacles and fucoids (moderately exposed shores)

Description

On moderately exposed rocky shores the extent of fucoid cover is typically less than that found on sheltered shores (SLR.F). The fucoids form a mosaic with barnacles on bedrock and boulders, rather than the blanket cover associated with sheltered shores, except on the lower shore where there may be dense Fucus serratus (MLR.Fser). Beneath the band of lichens at the top of the shore (LR.YG and LR.Ver) the channel wrack Pelvetia canaliculata typically occurs overgrowing the black lichen Verrucaria spp. with sparse barnacles (MLR.PelB). Below, barnacles and limpets Patella may cover extensive areas of rock (ELR.BPat), particularly on steep or vertical rock. In the absence of ELR.BPat, the spiral wrack Fucus spiralis may occur (SLR.Fspi). On the mid shore the bladder wrack Fucus vesiculosus generally forms a mosaic with barnacles (MLR.FvesB). Finally, the serrated wrack Fucus serratus, dominates the lower shore (MLR.Fser); a number of sub-biotopes have been described: lower shore bedrock and boulders may be characterized by mosaics of Fucus serratus and turf-forming red algae (MLR.Fser.R); where the density of Fucus serratus is greater (typically common - superabundant) and the abundance of red algae less MLR.Fser.Fser should be recorded. The presence of boulders and cobbles on the shore can increase the micro-habitat diversity which often results in a greater species richness. (Information taken from the Marine Biotope Classification for Britain and Ireland, Version 97.06: Connor et al., 1997a, b).

Recorded distribution in Britain and Ireland

In Britain and Ireland, barnacle and fucoid biotopes are widespread on bedrock and boulder shores exposed to strong to moderate wave action and on steeply sloping or vertical rock on more sheltered shores.

Depth range

Lower shore, Mid shore, Upper shore

Additional information

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Habitat review

Ecology

Ecological and functional relationships

Ecological relationships within this biotope are very complex resulting in dynamic communities with a mosaic of patches of fucoid cover, dense barnacles and limpets subject to small scale temporal variations due to seasonal and non-seasonal factors. While physical factors clearly influence the distribution and abundance of species on rocky shores it is the interaction between physical and biological factors that is responsible for much of the structure and dynamics of rocky shore communities.
  • The diversity of species within the MLR.BF biotope, and on rocky shores in general, increases towards the lower shore where the habitat is wet for longer. Macroalgal cover increases the structural complexity of the habitat providing refugia for a wide range of mobile and sessile animals. The MLR.BF biotope occurs in the eulittoral zone, extending from the upper shore where barnacles and limpets are present in quantity with fucoids although often this belt has only sparse algal cover compared with the lower eulittoral.
  • Grazing on rocky shores can exert significant controlling influences on the algal vegetation, particularly by patellid limpets and littorinid snails which are usually the most prominent grazers. There are probably also significant effects caused by 'mesograzers' - amphipods such as Hyale prevostii and isopods, which are much smaller but may occur in high densities.
  • Predation can be an important force in the structuring of rocky shore communities. However, there are relatively few species or abundance of predators on rocky shores, a reflection of the species position at the top of the food web. The most obvious predator on rocky shores, particularly those exposed to wave action, is the whelk Nucella lapillus. At lower levels on the shore, starfish may become abundant and are predators especially of mussels. Crabs are more hidden from view on many rocky shores, often because they migrate up and down with the tides, or lurk in crevices at low tide. At low tide level the diversity of predators increases and nudibranch gastropods, polychaetes and nemertines may be abundant. Fish and birds, which invade the shore at high and low tide respectively, are also important predators on the shore.
  • In addition to barnacles, other sessile suspension feeding animals may be abundant on the lower shore in barnacle-fucoid biotopes. Organisms such as tunicates, sponges, bryozoans, hydroids and spirorbid worms are typically found on various parts of macroalgal plants or attached to the bedrock.
  • The presence of a fucoid canopy inhibits the settlement of barnacles by blocking larval recruitment mainly by 'sweeping' the rock of colonizers. However, the canopy offers protection against desiccation which promotes the clumping of adults and the recruitment of young in several species of mobile animals. The number of limpets increases with maturing fucoid clumps.
  • Limpets are the dominant grazers in the system and their home scars tend to be aggregated with a preference for mature algal patches. A spatially uneven pattern of grazing pressure is thought to lead to new algal patches in areas of low local limpet density (Hartnoll & Hawkins, 1985).
  • A dense covering of barnacle species is effective in limiting the efficiency of limpet grazing which adversely affects limpet growth. The development of an increasing barnacle cover would contribute, together with decreased limpet grazing to the re-establishment of the fucoid canopy.
  • The dense beds of fucoid plants provide substratum and shelter for a very wide variety of species, including the tube worm Spirorbis spirorbis, herbivorous isopods, such as Idotea, and amphipods like Hyale prevostii, and surface grazing snails, such as Littorina obtusata, and also provide considerable substratum for epiphytic species. They may also act as nursery grounds for various species including Nucella lapillus.

Seasonal and longer term change

Fucoid-barnacle mosaics on rocky shores are highly variable in space and time and considerable natural change is seen, especially in seaweed cover and number of limpets (Hartnoll & Hawkins, 1985). Natural changes can easily cause a given area to progress through a number of biotopes over time. Seasonal changes are also apparent on rocky shores with seasonal variation in growth and recruitment. Fucus serratus plants, for example, lose fronds in the winter, followed by regrowth from existing plants in late spring and summer, so that summer cover can be about 250% of the winter level (Hawkins & Hartnol, 1980). The barnacle population can be depleted by the foraging activity of the dog whelk Nucella lapillus from spring to early winter and replenished by settlement of Semibalanus balanoides in the spring and Chthamalus spp. in the summer and autumn.

Habitat structure and complexity

Barnacle-fucoid shores provide a variety of habitats and refugia for other species. Macroalgae increases the structural complexity of the habitat providing a variety of resources that are not available on bare rock. Fronds provide space for attachment of encrusting or sessile epifauna and epiphytic algae and provide shelter from wave action, desiccation and heat for invertebrates. Empty barnacle shells provide shelter for small littorinids such as Littorina neglecta and Littorina saxatilis.

The littoral community of fucoids, barnacles and limpets on moderately exposed shores is relatively unstable, existing in a state of dynamic equilibrium in which biological or physical changes can create quite drastic effects on the pattern of the community (Southward & Southward, 1978) and so the biotope itself is subject to change and may cycle between different biotopes or sub-biotopes.

Productivity

Rocky shore communities are highly productive and are an important source of food and nutrients for members of neighbouring terrestrial and marine ecosystems (Hill et al., 1998). Macroalgae exude considerable amounts of dissolved organic carbon which are taken up readily by bacteria and may even be taken up directly by some larger invertebrates. Only about 10% of the primary production is directly cropped by herbivores (Raffaelli & Hawkins, 1999). Dissolved organic carbon, algal fragments and microbial film organisms are continually removed by the sea. This may enter the food chain of local, subtidal ecosystems, or be exported further offshore. Rocky shores make a contribution to the food of many marine species through the production of planktonic larvae and propagules which contribute to pelagic food chains.

Recruitment processes

Many rocky shore species, plant and animal, possess a planktonic stage: gamete, spore or larvae which float in the plankton before settling and metamorphosing into adult form. This strategy allows species to rapidly colonize new areas that become available such as in the gaps often created by storms. For these organisms it has long been evident that recruitment from the pelagic phase is important in governing the density of populations on the shore (Little & Kitching, 1996). Both the demographic structure of populations and the composition of assemblages may be profoundly affected by variation in recruitment rates.
  • Community structure and dynamics on barnacle-fucoid shores are strongly influenced by larval supply. Annual variation in recruitment success, of algae and barnacles particularly, can have a significant impact on the patchiness of the shore. For example, a low recruitment of limpets, or high recruitment of barnacles might lead to reduced limpet grazing and, therefore, more Fucus spp. escapes resulting in a fucoid dominated community.
  • Recruitment of Fucus serratus from minute pelagic sporelings takes place from late spring until October. There is a reproductive peak in the period August - October and plants can be dispersed long distances (up to 10km). Germlings have a high mortality during winter due to storms and heavy wave action with up to 83% being recorded lost in 77 days on the Isle of Man.
  • Ascophyllum nodosum is also recruited from pelagic sporelings, but recruitment is generally poor with few germlings found on the shore.
  • Barnacle recruitment can be very variable because it is dependent on a suite of environmental and biological factors, such as wind direction and success depends on settlement being followed by a period of favourable weather. Long term surveys have produced clear evidence of barnacle populations responding to climatic changes. During warm periods Chthamalus spp. predominate, whilst Semibalanus balanoides does better during colder spells (Hawkins et al., 1994). Release of Semibalanus balanoides larvae takes place between February and April with peak settlement between April and June. Release of larvae of Chthamalus montagui takes place later in the year, between May and August.
  • Recruitment of Patella vulgata fluctuates from year to year and from place to place. Fertilization is external and the larvae is pelagic for up to two weeks before settling on rock at a shell length of about 0.2mm. Winter breeding occurs only in southern England: in the north of Scotland it breeds in August and in north-east England in September.
  • Among sessile organisms, patterns fixed at settlement, though potentially altered by post settlement mortality, obviously cannot be influenced by dispersal of juveniles or adults.
Some of the species living in the biotope do not have pelagic larvae, but instead have direct development of larvae producing their offspring as 'miniature adults'. For example, many whelks such as Nucella lapillus and some winkles do this, as do all amphipods. Adult populations of these species are governed by conditions on the shore and will generally have a much smaller dispersal range than species with a pelagic larvae.

Time for community to reach maturity

Although the recruitment of many species in the barnacle-fucoid mosaics is rapid, the time scale for recovery of rocky shore communities following mass mortalities caused by oil dispersants used in the Torrey Canyon oil spill clean-up was at least 10 years. However, when considering limpet population structure and barnacle densities then the time to return to levels of spatial and temporal variation normally seen on barnacle-fucoid shores was closer to 15 years. (Hill et al., 1998).

Additional information

Moderately exposed rocky shores are often made up of a mosaic of communities, each cycling through a number of successional stages and structured by a number of positive and negative interactions between the main species but with fluctuations generated by recruitment variation. These communities are each dominated by a particular group of species, which may give way to others and sometimes to bare rock over time so that the MLR.BF biotopes may represent one stage in a progression of biotopes.

Preferences & Distribution

Recorded distribution in Britain and IrelandIn Britain and Ireland, barnacle and fucoid biotopes are widespread on bedrock and boulder shores exposed to strong to moderate wave action and on steeply sloping or vertical rock on more sheltered shores.

Habitat preferences

Depth Range Lower shore, Mid shore, Upper shore
Water clarity preferences
Limiting Nutrients Nitrogen (nitrates), Phosphorus (phosphates)
Salinity Full (30-40 psu)
Physiographic Open coast
Biological Zone Eulittoral
Substratum Bedrock, Large to very large boulders, Small boulders
Tidal
Wave Moderately exposed
Other preferences None found

Additional Information

Changes in the relative abundance of the cold-water barnacle Semibalanus balanoides and its warm-water counterparts Chthamalus stellatus and Chthamalus montagui show strong links with climatic conditions (Southward et al., 1995).

Species composition

Species found especially in this biotope

    Rare or scarce species associated with this biotope

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    Additional information

    No text entered.

    Sensitivity reviewHow is sensitivity assessed?

    Explanation

    The seaweeds Fucus serratus and Ascophyllum nodosum and the barnacle Semibalanus balanoides are the key structural species for barnacle and fucoid shores. Patella vulgata is the dominant grazer in the biotope and contributes to the regulation of algal patches. The amphipod Hyale prevostii has been included because it is a characteristic species of fucoid dominated rocky shores, an important mesograzer and because amphipods are generally regarded as sensitive species. In undertaking an assessment of sensitivity of this biotope, account is taken of knowledge of the biology of all characterizing species in the biotope. However, the selected 'indicative species' are particularly important in undertaking the assessment because they have been subject to detailed research.

    Species indicative of sensitivity

    Community ImportanceSpecies nameCommon Name
    Key structuralAscophyllum nodosumEgg wrack
    Key structuralFucus serratusToothed wrack
    Important otherHyale prevostiiAn amphipod
    Key functionalPatella vulgataCommon limpet
    Key structuralSemibalanus balanoidesAn acorn barnacle

    Physical Pressures

     IntoleranceRecoverabilitySensitivitySpecies RichnessEvidence/Confidence
    High High Moderate Major decline High
    All key and important species in the biotope are highly intolerant of substratum loss. The algae and barnacles are permanently attached to the substratum so populations would be lost. Epifaunal grazers like Patella vulgata and littorinid snails are epifaunal and substratum loss causes increased risk of desiccation and predation and so populations are unlikely to survive. Mobile species like the amphipod Hyale prevostii will be indirectly affected by the loss of fucoid plants as will sessile epiphytic flora and fauna. Recovery is good because recruitment of key species, with the exception of Ascophyllum nodosum, is fairly rapid so that the biotope will look much as before within five years. However, it can take between 10 and 15 years for the natural variation in community structure of the biotope to return to normal after significant mortality of key species such as seen after the Torrey Canyon oil spill (Southward & Southward, 1978).
    Intermediate High Low Decline High
    A 5cm layer of sediment or debris on a barnacle and fucoid shore is likely to reduce photosynthesis of algae and may cause some plants to rot. Sediment will have an especially adverse effect on young germling algae and on the settlement of larvae and spat. Barnacle feeding may be affected and limpet locomotion and grazing may be impaired. Lower down the shore active suspension feeders such as sponges and mussels may be killed by smothering. However, since wave action on rocky shores is likely to mobilise sediment alleviating the effect of smothering intolerance has been assessed as intermediate. Most characterizing species have planktonic larvae and/or are mobile and so can migrate into the affected area so recovery should be high.
    Low High Low Minor decline Moderate
    The biotope is likely to have some tolerance of suspended sediment and siltation as it is also found on sheltered shores where siltation may occur and key species in the biotope have low intolerance to the factor. However, suspended sediment may clog respiratory and feeding organs of other species such as sea squirts and spirorbid worms and so epifaunal species composition may change if suspended sediment changes significantly.
    Intermediate High Low Decline Moderate
    A change in desiccation equivalent to a change in position of one vertical biological zone on the shore is likely to change the distribution of the biotope because the key structural algal species can only tolerate desiccation up to a critical level of water content. The upper limit of fucoids will be depressed by an increase in desiccation and the community composition here will change becoming dominated by barnacles and limpets so that the biotope may change from MLR.BF to ELR.MB.Bpat, for example. A decrease in the level of desiccation may result in the upper limit of the biotope extending further up the shore. Most species living below the fucoid canopy will be protected by them from the worst effects of desiccation. Sponges, such as Halichondria panicea, are likely to withstand some desiccation as they hold water. The upper limit of many species however, is likely to be depressed. Sub-biotopes on the upper shore are likely to be less intolerant of changes in desiccation that those on the low shore.
    Intermediate High Low Decline High
    A change in the level of emergence on the shore will affect the upper or lower distribution limit of all the key species. Changes in the numbers of important species are likely to have profound effects on community structure and may result in loss of the biotope at the extremes of its range. For example, at the upper limit the biotope may lose fucoid cover and so change to one dominated by barnacles and limpets such as ELR.MB.Bpat.
    Intermediate High Low No change Moderate
    Significant increases in water flow rate may cause some of the macroalgal populations to be torn off the substratum. On the lower shore however, increased water movement encourages several filter feeding faunal groups, such as sponges and ascidians, to occur and species richness may increase. The effect of a decrease in water flow rate is likely to be low because the biotope is also found on shores with low water flow. However, barnacle growth rates are lower in reduced water flow and this may affect the balance of the barnacle-fucoid mosaic, perhaps promoting fucoid dominated shores such that MLR.BF becomes replaced by another biotope such as SLR.Fserr.
    Intermediate High Low Minor decline Moderate
    The biotope occurs in warmer and colder parts of Britain and Ireland and similar assemblages of species are known to occur in Norway, Canada and Brittany so that long-term temperature change is unlikely to cause a change in biotope. Schonbeck & Norton (1979) demonstrated that fucoids can increase tolerance in response to gradual change in a process known as 'drought hardening'. However, fucoids are more intolerant of sudden changes in temperature and relative humidity with field observations of bleaching and death of plants during periods of hot weather (Hawkins & Hartnoll, 1985). All other key species are moderately tolerant of temperature changes at the benchmark level and so intolerance of the biotope is assessed as intermediate. Larvae and juvenile individuals are likely to be more intolerant of changes in temperature than adults. Changes in the numbers of the key structuring species are likely to have profound effects on community structure.
    Low High Low No change Moderate
    intolerance to turbidity is low because the key species are relatively tolerant of changes in turbidity and the biotope is also found in areas of low water flow where turbidity is likely to be high. An increase in turbidity may reduce algal growth rates because of increased light attenuation although because photosynthesis also occurs during emersion the effect may not be significant. There may be some clogging of suspension feeding apparatus in some species although characteristic species survive in occasionally very turbid conditions and increased turbidity often means an increase in available food particles.
    High High Moderate Decline High
    The effect of changes in wave action on barnacle and fucoid community stability is predominantly through its influence on the balance of the biological interactions. In increasing wave action, fucoids may be removed and grazers and barnacles are favoured at the expense of the fucoids, and a stable situation with minimal fucoid cover prevails. Ascophyllum nodosum, in particular is very intolerant of increased wave exposure. Conversely, if wave exposure reduces fucoids are favoured and maintain a more or less total and permanent canopy (Hartnoll & Hawkins, 1985). Thus, if wave exposure changes the biotope can rapidly disappear to be replaced by another, barnacle dominated on extremely exposed shores (A1.113) and dense fucoid cover on sheltered shores (SLR.F.Fser). The loss of fucoid plants results in the loss of structural complexity and invertebrate species diversity may decline in the absence of microhabitats and refugia.
    Tolerant Not relevant Not relevant No change Very low
    None of the selected key or important species in the biotope are recorded as sensitive to noise although limpets and amphipods do respond to vibration. However, the biotope as a whole is not likely to be sensitive to changes in noise levels.
    Tolerant Not relevant Not relevant Not relevant Very low
    Algae have no visual perception. Most macroinvertebrates have poor or short range perception and are unlikely to be affected by visual disturbance such as by boats or humans.
    High High Moderate Decline Moderate
    The rocky intertidal is not at risk from boating activity but is susceptible to abrasion and physical impact from trampling. Even very light trampling on shores in the north east of England was sufficient to reduce the abundance of fucoids (Fletcher & Frid, 1996) which, in turn reduced the microhabitat available for epiphytic species. Trampling damage is particularly serious for the long-lived but slowly recruiting Ascophyllum nodosum. Light trampling pressure, of 250 steps in a 20x20 cm plot, one day a month for a period of a year, has also been shown to damage and remove barnacles (Brosnan & Crumrine, 1994). Trampling pressure can thus result in an increase in the area of bare rock on the shore (Hill et al., 1998). Chronic trampling can affect community structure with shores becoming dominated by algal turf or crusts. However, if trampling stops, recovery should be good. In Oregon for example, the algal-barnacle community recovered within a year after trampling stopped (Brosnan & Crumrine, 1994).
    High High Moderate Major decline Very low
    intolerance to displacement is high because many of the key species in the biotope, including Fucus serratus, Ascophyllum nodosum and Semibalanus balanoides are permanently attached to the substratum and cannot re-establish themselves if detached. Loss of the key species results in loss of the biotope. Removal of the fucoid canopy would create an increased risk of desiccation (see above) for the understory foliose red algae and macroinvertebrates resulting in a significantly reduced species diversity. In general recovery is good because the species have pelagic larvae although recruitment of Ascophyllum nodosum is poor. Removal of space occupying individuals provides room for new individuals to colonize and bare rock is often initially colonized by barnacles.

    Chemical Pressures

     IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
    High High Moderate Major decline Moderate
    intolerance of the biotope is assessed as high because two of the key species, Fucus serratus and Patella vulgata are highly intolerant of synthetic chemicals. Fucus serratus was found to be intolerant of three biocides likely to be found in the marine environment (Scanlon & Wilkinson, 1987) and fucoids in general are reported to exhibit high intolerance to chlorate and pulp mill effluents containing chlorate (Kautsky, 1992). Patella vulgata is extremely intolerant of aromatic solvent based dispersants such as those used in the Torrey Canyon oil spill clean-up (Smith, 1968). On rocky coasts of Amlwch in areas close to acidified halogenated effluent from a bromine plant the shore consisted almost entirely of bare rock but there was a fucoid-barnacle mosaic nearby (Hoare & Hiscock, 1974).
    Heavy metal contamination
    Low High Low Decline Very low
    intolerance of the biotope is low because the key structural and functional species are fairly robust in terms of heavy metal pollution. Adult plants of Fucus serratus and Ascophyllum nodosum appear to be fairly tolerant of heavy metal pollution although earlier life stages may be more sensitive (Holt et al., 1997). Barnacles are able to concentrate heavy metals in their tissues and Patella vulgata is found living in conditions of fairly high metal contamination in the Fal estuary in Cornwall (Bryan & Gibbs, 1983). Recovery of all species is high although a return to normal community structure variation may take as much as 10-15 years (Southward & Southward, 1978).
    Hydrocarbon contamination
    Intermediate High Low Major decline Moderate
    The loss of key herbivores, such as limpets and littorinids, and the subsequent prolific growth of ephemeral algal mats appears to be a fairly consistent feature of coastal oil spills (Hawkins & Southward, 1992). Species richness, diversity and evenness were all much lower at sites close to the Braer oil spill (Newey & Seed, 1995). In the absence of tarry masses of oil which cause physical smothering of sessile animals and mechanical damage to algae, the adult organisms occupying primary space in the barnacle-fucoid community are relatively resistant to damage from chemical properties of the oil itself, although some damage will inevitably occur. The most serious effects tend to occur among juvenile and newly settling recruits to the community, as well as the small crustaceans, such as the amphipod Hyale prevostii, associated with the dominant intertidal algal species. Recovery should be high because wave action will remove oil from rocky shores and a dispersive larval stage of the key species enables rapid recolonization. However, for severely impacted rocky shore community recovery may be extremely slow, and 10 years or more may elapse before normal community structure and variability have been restored (Southward & Southward, 1978).
    Radionuclide contamination
    No information No information No information Insufficient
    information
    Not relevant
    Insufficient
    information.
    Changes in nutrient levels
    Intermediate High Low Decline Low
    A reduction in the level of nutrients could reduce growth rates of algal species in the biotope. Nutrient availability is the most important factor controlling germling growth. A slight increase in nutrients may enhance growth rates but high nutrient concentrations could lead to the overgrowth of the algae by ephemeral green algae and an increase in the number of grazers. The effect of sewage discharge on a moderately exposed rocky shore is generally low because water movements should limit the build up of particulates and prevents eutrophication. Fucoids appear to be relatively resistant to the input of sewage, and grow apparently healthily to within 20 metres of an outfall discharging untreated sewage in the Isle of Man (Holt et al., 1997). However, on more sheltered barnacle and fucoid shores increased eutrophication has been demonstrated to lead to increased growth of filamentous brown or green algae both on rocks and epiphytically which can reduce fucoid growth, increase grazer levels such that they become damaging to the fucoids, and prevent development of the young stages of fucoid algae (Kautsky, 1991). Loss of fucoid algae will result in the loss of the biotope so intolerance is assessed as intermediate.
    Low High Low Minor decline Low
    Barnacle and fucoid shores are able to tolerate short term variations in salinity because the littoral zone is regularly exposed to precipitation. All key species are able to penetrate into lower salinity estuarine waters, down to about 20psu so the biotope can tolerate long term reductions in salinity within its normal tolerance range although growth rates and fecundity are likely to be impaired. However, some of the other species within the biotope may be highly intolerant of changes in salinity resulting in a loss of diversity. However most species have planktonic larvae so recolonization and recovery should be high.
    Intermediate High Low Decline Very low
    Cole et al. (1999) suggest possible adverse effects on marine species below 4 mg/l and probable adverse effects below 2 mg/l. There is no information about key algae species tolerance to changes in oxygenation although Kinne (1972) reports that reduced oxygen concentrations inhibit both algal photosynthesis and respiration. Sensitive species, such as the amphipod Hyale prevostii, may be lost resulting in a reduction in diversity.

    Biological Pressures

     IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
    Intermediate High Low Minor decline Very low
    The cryptoniscid isopod Hemioniscus balani is a widespread parasite of barnacles, found around the British Isles. Heavy infestation inhibits or destroys the gonads resulting in castration of the barnacle. High levels of infestation may reduce barnacle abundance and distribution which would impact on patch dominance although no reported cases of this were found.
    Low High Low No change Low
    The Australasian barnacle Elminius modestus does well in estuaries and bays where it can displace the native Semibalanus balanoides. Its overall effect on the dynamics of rocky shores has however, been small as Elminius modestus has simply replaced some individuals of a group of co-occurring barnacles (Raffaelli & Hawkins, 1999).
    Intermediate High Low Decline Low
    Both Fucus serratus and Ascophyllum nodosum are harvested within the UK and the extraction of either of these species will have a significant impact on community structure of the biotope. Removal of algal species will result in loss of micro-habitats for other species and, hence, a reduced faunal diversity. However, the loss will favour the barnacles which would be expected to increase in abundance. It is extremely unlikely that any of the other species indicative of sensitivity would be targeted for extraction and overall, an intermediate intolerance has been suggested.

    Recovery should be high because the key species have a dispersive larval stage and reproduce every year. However, a return to normal community structure dynamics after removal of all key species appears to take much longer, 10 and possibly up to 15 years (Southward & Southward, 1978).

    Intermediate High Low No change Very low

    Additional information

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    Importance review

    Policy/Legislation

    Habitats Directive Annex 1Reefs

    Exploitation

    • Barnacle and fucoid shores are widely exploited for a range of recreational uses including rock pooling, angling and as a resource for students and scientific researchers. Trampling has been shown to have a significant impact on community structure.
    • Fucoid plants are collected, dried and used as a soil additive. Various fucoid algae are used in the production of alginates for use in the pharmaceutical and cosmetics industries.

    Additional information

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    Bibliography

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    Citation

    This review can be cited as:

    Hill, J.M. 2000. Barnacles and fucoids on moderately exposed shores. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. Available from: http://www.marlin.ac.uk/habitat/detail/33

    Last Updated: 01/10/2000